WASHINGTON (REUTERS) - The White House said on Thursday that more than 6 million people have now signed up for private insurance plans under President Barack Obama's signature healthcare law known as Obamacare, reflecting a surge in enrollments days before the March 31 deadline.

Ten days ago, the administration had pegged enrollment at more than 5 million people, and enlisted celebrities and top government officials to try to convince more uninsured people - particularly the young and healthy - to sign up.

The last-minute boost has exceeded the nonpartisan Congressional Budget Office's estimate that 6 million people would sign up in the program's first year, down from earlier expectations of 7 million enrollees because of problems with websites used for shopping for insurance.